1. Field
Embodiments of the present disclosure relate to heteroepitaxial growth of materials with high lattice mismatch. More particularly, embodiments of the present disclosure relate to reducing dislocation density in a heteroepitaxial growth film and devices including heteroepitaxial films with reduced dislocation density.
2. Description of the Related Art
Heteroepitaxy, a crystalline film growth on a crystalline substrate or film of a different material, has many practical applications. For example, germanium (Ge) heteroepitaxy on silicon (Si) is used as p-channel in field effect transistors (FET). However, heteroepitaxy films are prone to defects, such as dislocations, anti-phase boundaries, and stacking faults, due to the lattice mismatch between the two different crystalline materials.
Aspect ratio trapping (ART) has been used to reduce defects in heteroepitaxy films. In aspect ratio trapping, a crystalline material grows in deep, narrow trenches, i.e. high aspect ratio trenches, so that some dislocations caused by lattice mismatch may terminate at the trench walls, thus, trapped within the high aspect ratio trenches rather than running up into active area of the crystalline material.
However, conventional aspect ratio trapping cannot terminate dislocations generated in along the length of the narrow trenches. FIG. 1 schematically illustrates a structure 100 of conventional aspect ratio trapping. A narrow trench 106 is formed in a dielectric layer 104 over a crystalline material 102 so that a heteroepitaxy film may be formed in the narrow trench 106. The narrow trench 106 is narrow along the x direction and extends in length along the z direction. The crystalline material 102 exposed at a bottom 110 of the narrow trench 106 serves as the seed structure for the epitaxial growth of a guest material in the narrow trench 106. During heteroepitaxy, dislocations caused by mismatch between the lattices of the guest material and the crystalline material 102 generate from the bottom 110 and expand along all directions. The dislocations expanding along x-y plane, i.e. perpendicular to the length of the narrow trench 106, may run into sidewalls 108 and be terminated. However, dislocations expanding along x-z plane, i.e. parallel to the length of the narrow trench 106, may run up to a top 112 of the narrow trench 106 and negatively affect the intended active area.
Therefore, there is a need for methods and structures with reduced defects in heteroepitaxy film.